A fullerene that is typical in C.sub.60 is bonded through Van der Waals force and has a football like shape of high symmetry. All the carbon atoms in one molecule are equivalent and bonded through covalent bond to each other to form a very stable crystal. Fullerenes such as C.sub.60 or the like can be considered to take a fcc structure crystallographically, accordingly they show metal like mechanical properties such as plastic deformation, work hardening or the like. Based on such properties, as a new carbon-based material, various applications of the fullerenes are expected. In addition, based on the properties of the fullerene itself, applications in superconducting material, catalytic material, lubricant material, bio-material, non-linear optics material or the like are being studied.
So far, the fullerenes such as C.sub.60 has been prepared by arc discharge method that utilizes a carbon rod or particulate carbon as an electrode, or by laser ablation method in which a beam of UV laser is irradiated on surface of graphite. Since fullerenes are formed in soot mixed therein, they are extracted by the use of a collector that employs a filter, benzene or the like.
In the material piled up at a cathode side during the above described arc discharge, there are included fullerenes of higher order (giant fullerene) called such as carbon nano-capsule or carbon nano-tube. After crushing the material piled up at the cathode side, they can be obtained by refining with an organic solvent such as ethanol or the like. Both the carbon nano-capsule and carbon nano-tube has a hollow structure. By encapsulating another metallic atom or a micro-crystallite in the hollow inside of such a giant fullerene, synthesis of a new material or search of a new function is being carried out.
As a giant fullerene in which another metallic atom or a micro-crystallite is encapsulated in the hollow inside of the carbon nano-capsule or carbon nano-tube (hereinafter refer to as an endohedral giant fullerene), ones in which fine particles of carbides of rare earth metals such as La, Y or the like, or fine metallic particles of Fe, Co, Ni or the like are encapsulated have been reported. These are prepared by use of the arc discharge method with a carbon electrode that includes powder of a metal or an oxide, and by refining thereafter the endohedral giant fullerene included in the deposits piled up at the cathode.
As one kind of the giant fullerene, substances called an onion-like graphite in which fullerenes of larger molecular weight are superposed concentrically outside a core consisting of C.sub.60 or the like to form external shells have been discovered. It is being studied to prepare an endohedral giant fullerene by use of such an onion-like graphite. The endohedral giant fullerenes, based on their properties, are expected to apply in device materials such as material for electronic parts, sensor material, filter material or the like, and new functional materials such as superconducting material, bio-material, medical material or the like.
The conventional giant fullerenes or endohedral giant fullerenes, however, are included in the deposit that is produced by the arc discharge method as described above. Accordingly, they can be separated with difficulty from impurities such as graphite like substance or amorphous carbon. In the endohedral giant fullerene, there is a problem that shape or state of encapsulation can not be easily controlled. Further, fine particles being encapsulated in the giant fullerene are restricted, at present, to particular metallic particles or compound particles.
In particular, when considering an application of the giant fullerenes or endohedral giant fullerenes in a device or a new functional material, it is important to enable to control the magnitude of a single giant fullerene or the position where the giant fullerene itself is formed. In addition, the state of formation of the giant fullerenes such as state of connection between the giant fullerenes or structures thereof is also important to be controlled. However, the conventional manufacturing method does not allow controlling them easily.
In addition, since the giant fullerene is unstable substance, some means is required to implement to protect the generated giant fullerene. However, at the present time, such a technology has not been found.
An object of the present invention is to provide a fullerene containing structure that allows to control the shape or the positions to be formed together with the state of formation such as the connecting structure or the like with a relatively simple process, and that protects the generated fullerenes with a stable substance, and to provide a manufacturing method thereof.